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Research Cruise Aimed at Better Understanding of Hawaii Bottomfish

August 28, 2011

Scientists aboard the NOAA Ship Oscar Elton Sette are engaged in a 15 day research expedition to study the
biology of bottomfish stocks off the Kohala and Kona coasts of the Island of Hawaii ("Big Island"). The primary
purpose of the cruise is to collect adult specimens of the "Deep 7" bottomfish species (opakapaka, onaga, ehu,
lehi, gindai, kalekale, and hapu'upu'u) for on-going life history studies. Particular objectives of the life
history research are to determine the length and age at which these deepwater species become reproductively mature,
how fast they grow, and how long they are likely to live. The bottomfish specimens will be collected using
handline fishing gear deployed from small boats launched from the Sette. Specimen collection will focus on
opakapaka and gindai. Knowledge of growth rate and reproductive life history traits will enable PIFSC scientists
to better assess the stock status of these commercially and recreationally important bottomfish. More accurate
stock assessments will improve the scientific basis for bottomfish fishery management.

Researchers will collect specimens of gindai and other bottomfish species to learn more about their
growth rates, maturation, and longevity.

During the cruise, running from August 28 to September 11, Chief Scientist Robert Humphreys will lead a diverse
research team that includes scientists from the NOAA Fisheries Pacific Islands Fisheries Science Center in Honolulu,
the University of Hawaii Joint Institute for Marine and Atmospheric Research, Monterey Bay Aquarium, and the
University of Nations in Kailua-Kona.

In addition to collecting adult bottomfish specimens using handlines, the scientific field party will conduct
research to learn more about the little-known early life history of Deep-7 bottomfish in the waters off west Hawaii.
Subsurface plankton net tows (using an Isaacs-Kidd trawl) will be conducted during daylight hours to collect
larvae of these fishes. Larger larvae and early pelagic juveniles of Deep-7 bottomfish will be collected from
subsurface depths using a Cobb midwater trawl during the evening.

An Isaacs-Kidd trawl will be deployed from the NOAA Ship Oscar Elton Sette to collect eggs and larvae
of bottomfish and billfish in surface waters of the ocean.

Although the focus of the cruise is to study bottomfish, surface Isaacs-Kidd net tows will also be conducted to
collect specimens of billfishes in their early life stages. These tows will target surface slicks off the Kona
coast where eggs and larvae become concentrated. Scientists will be able to learn more about which species of
billfish are spawning, when and where their eggs and larvae occur, and whether spawning is associated with certain
environmental conditions, such as sea surface temperature and salinity. To measure environmental conditions, the
research team will gather data on ocean temperature and salinity using a conductivity-temperature-depth (CTD)
instrument and information on the direction and velocity of subsurface currents using an acoustic Doppler current
profiler (ADCP).

By analyzing the biological data and oceanographic data gathered during this Sette expedition, NOAA
fisheries scientists hope to gain a better understanding of key factors that characterize the habitat of pelagic
stage larvae and juvenile bottomfish and affect patterns of billfish spawning. The information gained in the Big
Island studies may be applicable to other islands within the Hawaiian archipelago and may provide a foundation for
similar studies in other areas of the Pacific.